Lubricating oil composition

ABSTRACT

A lubricating oil composition is provided containing a base oil having a kinematic viscosity at 40° C. in the range of from 2 to 20 mm 2 /s and a viscosity index of 50 or more and a polymethacrylate, 
         wherein the lubricating oil composition has a kinematic viscosity at 40° C. in the range of from 22 to 95 mm 2 /s; a kinematic viscosity at 100° C. in the range of from 10 to 30 mm 2 /s; a pour point of −10° C. or less; a CCS viscosity at −20 ° C. of 2500 mPas or less; and a flash point of 140° C. or more.

FIELD OF THE INVENTION

The present invention relates lubricating oil compositions, in particular to hydraulic oil compositions. More specifically, the present invention relates to a hydraulic oil composition for use in a door closer or a floor hinge employed for opening/closing various types of doors.

BACKGROUND OF THE INVENTION

Door closers using hydraulic oil compositions are widely employed for door opening/closing. Such door closers slowly close a door which has been manually opened, and when the door is caused by a wind or the like to move abruptly, the door closer is required to have the function of slowing down the motion of the door lest it should close on a hand.

SUMMARY OF THE INVENTION

A lubricating oil composition is provided comprising a base oil having a kinematic viscosity at 40° C. in the range of from 2 to 20 mm²/s and a viscosity index of 50 or more and a polymethacrylate,

wherein the lubricating oil composition has a kinematic viscosity at 40° C. in the range of from 22 to 95 mm²/s; a kinematic viscosity at 100° C. in the range of from 10 to 30 mm²/s;

-   a pour point of −10° C. or less; -   a CCS viscosity at −20° C. of 2500 mPas or less; and -   a flash point of 140° C. or more.

A method of lubricating a door closer or a floor hinge using such lubricating oil composition is also provided.

DETAILED DESCRIPTION OF THE INVENTION

The door closer fundamentally comprises a cylinder, a piston and an orifice, and prevents the door from being abruptly closed due to the resistance generated by the passage of a hydraulic oil composition through the orifice.

Since the door closer uses a hydraulic oil composition, sometimes opening and closing of the door becomes difficult due to temperature fluctuations. For example, during high temperature in summer, the viscosity of a hydraulic oil composition is decreased and thus the hydraulic oil composition passes through the orifice in a shorter period of time, leading to abrupt closing of the door. In contrast, during low temperature in the cold season, the viscosity of a hydraulic oil composition is increased and it takes a longer period of time to pass through the orifice, thereby causing the problem that an unduly long period of time is required for closing the door, and also that an unduly large force is required for opening the door.

Ordinarily, for lubricating oil compositions in general, when viscosity is to be increased for the purpose of viscosity adjustment, a polymer having a large molecular weight is added to a mineral oil or a synthetic oil. However, if such a polymer having large molecular weight is added to the oil, although the viscosity of the oil at high temperature is increased, the viscosity under low temperature is also increased. Therefore, when the oil is used in machinery, problems sometimes occur, particularly when the machinery is operated at low temperature.

Further, mineral oil contains a wax component which is crystallized at low temperature, and such wax crystals grow with time and thereby lower flowability of the oil. As a result, the oil comes to have an increased viscosity or sometimes may even become solidified. In order to prevent such a wax component from being crystallized, a pour-point depressant which is adsorbed on the wax crystals and suppresses the growth of the crystals is generally used; however, there are cases where because of the pour-point depressant the viscosity of the oil does not increase at high temperatures.

Still further, after a door closer is fixed to a building, it is used for a long period of time, and during such period, there is a tendency for the hydraulic oil composition to deteriorate. The thus-deteriorated oil hardens the oil seal so that the hydraulic oil composition leaks and becomes reduced in quantity. As a result, there are cases in which the door closer does not function satisfactorily. In particular, in order to perform the opening and/or closing of a door smoothly, a typical hydraulic oil composition is a mineral oil or synthetic oil having a low viscosity, which also causes a problem of compatibility with the oil seal.

In addition, as per Japanese Laid-open Patent Application No. H. 5-747488 it has been pointed out that when a mineral oil having low viscosity is used, a large amount of viscosity index improving agent needs to be added to the oil in order to increase the viscosity, and a problem arises regarding flowability of the oil at low temperatures.

It is highly desirable to obtain hydraulic oil compositions which show little fluctuation of viscosity over low temperatures and high temperatures and which can operate in the same condition at any time.

The present invention provides lubricating oil composition, in particular a hydraulic oil composition, comprising a base oil having a kinematic viscosity at 40° C. in the range of from 2 to 20 mm²/s and a viscosity index of 50 or more and a polymethacrylate, wherein the lubricating oil composition has a kinematic viscosity at 40° C. in the range of from 22 to 95 mm²/s; a kinematic viscosity at 100° C. in the range of from 10 to 30 mm²/s; a pour point of −10° C. or less; a CCS (cold cranking shear) viscosity at −20° C. of 2500 mPas or less; and a flash point of 140° C. or more.

The polymethacrylate used in the lubricating oil composition of the present invention preferably has a weight average molecular weight in the range of from 150,000 to 700,000.

In the present invention, the lubricating oil composition, in particular the hydraulic oil composition, is uninfluenced by hot or cold and shows practically the same degree of viscosity whether at low temperature or high temperature and stays in the same condition at all times, thereby making it possible to achieve smooth operation in, for example, a door closer. Also, since the lubricating oil composition, in particular the hydraulic oil composition is compatible with oil seals, problems of oil leakage seldom occur even over long periods. In addition, apart from in door closers or floor hinges as referred to above, the lubricating oil composition of the present invention may be widely employed as hydraulic oil composition of various types.

In a preferred embodiment of the present invention, the lubricating oil composition, in particular the hydraulic oil composition, has a viscosity index of at least 260.

The base oil in the lubricating oil composition of the present invention may be conveniently chosen from mineral oils, synthetic oils and mixtures thereof.

Mineral oils that may be conveniently used include base oils manufactured by conducting one or more treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, or hydrorefining on the lubricating oil fraction obtained from the reduced pressure distillation of reduced crude obtained by atmospheric distillation of crude oil.

Various types of synthetic oil may be conveniently used as the synthetic oil. Examples of synthetic oils include so-called GTL (gas-to-liquid) base oils obtained by solvent dewaxing or contact dewaxing after synthesis using the Fischer-Tropsch process. Other examples of synthetic oils that may be conveniently used include poly-α-olefins (for example ethylene-propylene copolymers, polybutylenes, 1-octene oligomers, 1-decene oligomers, and hydrides thereof), alkyl benzenes, alkyl naphthalenes, monoesters (for example, butyl stearate or octyl stearate), diesters (for example, ditridecyl glutarate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate, dioctyl sebacate, or dioctyl azelate), polyesters (for example, trimellitate esters), polyol esters (for example, trimethylol propane caprylate, trimethylol propane pelargonate, pentaerythritol-2-ethyl hexanoate, or pentaerythritol pelargonate), polyphenyl ethers and dialkyl diphenyl ethers.

The kinematic viscosity at 40° C. of the base oil is generally in the range of from 2 to 20 mm²/s, preferably in the range of from 5 to 15 mm²/s.

If the kinematic viscosity of the base oil exceeds 20 mm²/s, when the above polymethacrylate is added, the high-temperature kinematic viscosity of the lubricating oil composition may become too high, or, if polymethacrylate is added in an amount in accordance with the required high-temperature viscosity, the low temperature flowability may become poor due to the base oil failing to reach the necessary viscosity index mentioned below, due to paucity of addition of polymethacrylate.

On the contrary, if the kinematic viscosity of the base oil is less than 2 mm²/s, then the viscosity-increasing effect may become poor at more than a certain added content of the polymethacrylate, even if polymethacrylate is added in accordance with the prescribed high-temperature viscosity, and on the other hand the low-temperature viscosity may become large, with the result that the required low-temperature flowability cannot be obtained, or problems arise regarding safety in that the flash point becomes less than 140° C.

The viscosity index of the above base oil used in the lubricating oil composition of the present invention is generally 50 or more and preferably 70 or more. If the viscosity index of the base oil is low, then more polymethacrylate must be added in order to obtain the prescribed viscosity index, thereby lowering the solubility of the polymethacrylate at high temperature, with the possible consequence that the target viscosity index may not be achieved.

There are no particular restrictions regarding the upper limit of the viscosity index of the base oil, and for example base oils that may be used include normal paraffins, slack wax, GTL wax or a substance of viscosity index about 135 to 180, such as an isoparaffin-based mineral oil obtained by isomerisation.

The pour point of the above base oil is generally −10° C. or less, preferably −20° C. or less, more preferably −30° C. or less and most preferably −37.5° C. or less. If the pour point of the base oil is −10° C. or less, solidification of the hydraulic oil at low temperature can be prevented.

On the contrary, if the pour point is higher than −10° C., then even if polymethacrylate or a pour point depressant is added, it is difficult to obtain the necessary low temperature flowability for the lubricating oil composition.

The polymethacrylate that is added to the above base oil may be, for example, a non-dispersion type polymethacrylate or a dispersion type polymethacrylate. Non-dispersion type polymethacrylates include copolymers of one or more monomers selected from compounds expressed by the following general formula (1),

general formula (2),

and general formula (3),

and hydrides thereof.

Dispersion type polymethacrylates include, for example, copolymers of two or more monomers selected from compounds expressed by the following general formula (4),

and general formula (5),

or compounds obtained by introducing an oxygen-containing group into hydrides of these or copolymers of one or more 15 monomers selected from compounds expressed by the above general formula (1) to general formula (3) and one or more monomers selected from compounds expressed by the above general formula (4) or general formula (5) and hydrides thereof.

In the above general formula (1), R¹ represents a hydrogen atom or methyl group and R² represents an alkyl group having a carbon number in the range of from 1 to 18. Examples of alkyl groups having a carbon number in the range of from 1 to 18 represented by R² include: a methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group and octadecyl group (these alkyl groups may be of straight chain or branched form).

In the above general formula (2), R³ represents a hydrogen atom or methyl group and R⁴ represents a hydrocarbon group having a carbon number in the range of from 1 to 12. Examples of hydrocarbon groups having a carbon number in the range of from 1 to 12 represented by R⁴ include: alkyl groups such as a methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, or a dodecyl group, (these alkyl groups may be of straight chain or branched form); a cycloalkyl group having a carbon number in the range of from 5 to 7 such as a cyclopentyl group, cyclohexyl group, or a cycloheptyl group; an alkyl cycloalkyl group having a carbon number in the range of from 6 to 11 such as a methyl cyclopentyl group, dimethyl cyclopentyl group, methylethyl cyclopentyl group, diethyl cyclopentyl group, methyl cyclohexyl group, dimethyl cyclohexyl group, methylethyl cyclohexyl group, diethyl cyclohexyl group, methyl cycloheptyl group, dimethyl cycloheptyl group, methylethyl cycloheptyl group, or diethyl cycloheptyl group (the position of substitution of the alkyl groups in the cycloalkyl groups is not limited and may be chosen as required); an alkenyl group such as a butenyl group, pentenyl group, hexenyl group, heptenyl group, octenyl group, nonenyl group, decenyl group, undecenyl group, dodecenyl group (these alkenyl groups may be of straight chain or branched form and the position of the double bond is not limited and may be chosen as required); an aryl group such as a phenyl group or naphthyl group; an alkylaryl group having a carbon number in the range of from 7 to 12 such as a tolyl group, xylyl group, ethyl phenyl group, propyl phenyl group, butyl phenyl group, pentyl phenyl group, or hexyl phenyl group (these alkyl groups may be of straight chain or branched form, and the position of substitution into the aryl group is not limited and may be chosen as required); or an arylalkyl group having a carbon number in the range of from 7 to 12 such as a benzyl group, phenyl ethyl group, phenyl propyl group, phenyl butyl group, phenyl pentyl group, or phenyl hexyl group (these alkyl groups may be of straight chain or branched form).

In the above general formula (3), X¹ and X² are independently selected from a hydrogen atom, an alkoxy group —OR¹⁰ having a carbon number in the range of from 1 to 18 (wherein R¹⁰ is an alkyl group having a carbon number in the range of from 1 to 18) or a monoalkyl amino group —NHR¹¹ having a carbon number in the range of from 1 to 18 (wherein R¹¹ is an alkyl group having a carbon number in the range of from 1 to 18).

In the above general formula (4), R⁵ indicates a hydrogen atom or methyl group, R⁶ indicates an alkylene group having a carbon number in the range of from 1 to 18, Y¹ indicates an amine residue or heterocyclic residue containing from 1 to 2 nitrogen atoms and from 0 to 2 oxygen atoms, and a is 0 or 1.

The alkylene group having a carbon number in the range of from 1 to 18 indicated by R⁸ may be, for example, an ethylene group, a propylene group, butylene group, pentylene group, hexylene group, heptylene group, octylene group, nonylene group, decylene group, undecylene group, dodecylene group, tridecylene group, tetradecylene group, pentadecylene group, hexadecylene group, heptadecylene group or octadecylene group (these alkylene groups may be of straight chain or branched form).

Also, the group indicated by Y¹ may be, for example, a dimethylamino group, diethylamino group, dipropylamino group, dibutylamino group, anilino group, toluidino group, xylidino group, acetylamino group, benzoylamino group, morpholino group, pyrrolyl group, pyrrolino group, pyridyl group, methyl pyridyl group, pyrrolidinyl group, piperidinyl group, quinonyl group, pyrrolidonyl group, pyrrolidono group, imidazolino group or pyrazino group.

In the above general formula (5), R⁷ indicates a hydrogen atom or methyl group, and Y² indicates an amine residue or heterocyclic residue containing from 1 to 2 nitrogen atoms and from 0 to 2 oxygen atoms.

The group indicated by Y² may be, for example, a dimethylamino group, diethylamino group, dipropylamino group, dibutylamino group, anilino group, toluidino group, xylidino group, acetylamino group, benzoylamino group, morpholino group, pyrrolyl group, pyrrolino group, pyridyl group, methyl pyridyl group, pyrrolidinyl group, piperidinyl group, quinonyl group, pyrrolidonyl group, pyrrolidono group, imidazolino group or pyrazino group.

Preferred examples of one or more monomers selected from the compounds indicated by general formula (1) to general formula (3) include: alkyl acrylates having a carbon number in the range of from 1 to 18, alkylamide methacrylates having a carbon number in the range of from 1 to 18, olefins having a carbon number in the range of from 2 to 20, styrene, methyl styrene, maleic anhydride esters, maleic anhydride amides and mixtures thereof.

Preferred examples of one or more monomers selected from the compounds indicated by general formula (4) and general formula (5) include: dimethylamino methyl methacrylate, diethylamino methyl methacrylate, dimethylamino ethyl methacrylate, 2-methyl-5-vinyl pyridine, morpholino methyl methacrylate, morpholino ethyl methacrylate, N-vinyl pyrrolidone and mixtures thereof.

The copolymerisation mol ratio of a copolymer of one or more monomers selected from the compounds indicated by the above general formula (1) to general formula (3) to one or more monomers selected from the compounds indicated by general formula (4) and general formula (5) is typically about 80:20 to 95:5, respectively.

The method of manufacture of said copolymers is not limited, but, a copolymer can conveniently be obtained by radical solvent polymerisation of the monomers in the presence of a polymerisation initiator such as benzoyl peroxide.

The weight average molecular weight of the above polymethacrylate is preferably in the range of from 150,000 to 700,000, more preferably in the range of from 200,000 to 500,000, and is preferably selected taking into account the rate of increase of viscosity per unit mass and the rate of improvement of the viscosity index.

In the lubricating oil composition of the present invention, polymethacrylate is employed in an amount such as to produce a kinematic viscosity at 40° C. in the range of from 22 to 95 mm²/s and may be blended with a suitable amount of one or more compounds selected from the various types of polymethacrylate referred to above. If the kinematic viscosity at 40° C. is less than 22 mm²/s, the high-temperature viscosity is insufficient; on the other hand, if the CCS (cold-cranking shear) viscosity at −20° C. exceeds 2500 mPas, closure at a low temperature becomes slow, thereby presenting an obstacle to use.

A suitable content of polymethacrylate is added to the base oil in order to ensure that the kinematic viscosity of the above lubricating oil composition at 40° C. is within the above range. The amount of polymethacrylate is preferably in the range of from 0.1 to 30 weight %, with reference to the total weight of the lubricating oil composition.

The lubricating oil composition of the present invention, apart from the above base oil and polymethacrylate, may be conveniently blended with additional additives, for example, with anti-wear agents, antioxidants, rust inhibitors, corrosion inhibitors and/or anti-foaming agents.

Anti-wear agents that may be conveniently used include phosphorus-based compounds, organic molybdenum compounds, fatty acid ester compounds and aliphatic amine based compounds.

Examples of phosphorus-based compounds that may be conveniently used include zinc alkyl thiophosphate, phosphoric acid, phosphorous acid, phosphoric acid monoesters, phosphoric acid diesters, phosphoric acid triesters, phosphorous acid monoesters, phosphorous acid diesters, phosphorous acid triesters, salts of phosphoric (phosphorous) acid esters, and thiophosphoric acid or thiophosphorous acid and esters thereof, as well as mixtures thereof.

The above components listed as phosphorus-based compounds, with the exception of phosphoric acid, thiophosphoric acid, phosphorous acid and thiophosphorous acid, are normally compounds containing a hydrocarbon group having a carbon number in the range of from 2 to 30, preferably in the range of from 3 to 20.

As such hydrocarbon groups having a carbon number in the range of from 2 to 30, there may be mentioned by way of example alkyl groups, cycloalkyl groups, alkyl cycloalkyl groups, alkenyl groups, aryl groups, alkylaryl groups and arylalkyl groups.

As said alkyl groups, there may be mentioned by way of example alkyl groups such as ethyl groups, propyl groups, butyl groups, pentyl groups, hexyl groups, heptyl groups, octyl groups, nonyl groups, decyl groups, undecyl groups, dodecyl groups, tridecyl groups, tetradecyl groups, pentadecyl groups, hexadecyl groups, pentadecyl groups and octadecyl groups (these alkyl groups may be of straight chain form or branched form).

As said cycloalkyl groups, there may be mentioned by way of example cycloalkyl groups having a carbon number in the range of from 5 to 7 such as a cyclopentyl group, cyclohexyl group or cycloheptyl group.

As said alkyl cycloalkyl groups, there may be mentioned by way of example alkyl cycloalkyl groups having a carbon number in the range of from 6 to 11 such as a methyl cyclopentyl group, dimethyl cyclopentyl group, methyl ethyl cyclopentyl group, diethyl cyclopentyl group, methyl cyclohexyl group, dimethyl cyclohexyl group, methyl ethyl cyclohexyl group, dimethyl cyclohexyl group, methyl cycloheptyl group, dimethyl cycloheptyl group, methyl ethyl cycloheptyl group and diethyl cycloheptyl group (the position of substitution of the alkyl group into the cycloalkyl group is not limited and may be chosen as required).

As said alkenyl groups, there may be mentioned by way of example alkenyl groups such as butenyl groups, pentenyl groups, hexenyl groups, heptenyl groups, octenyl groups, nonenyl groups, decenyl groups, undecenyl groups, dodecenyl groups, tetradecenyl groups, pentadecenyl groups, hexadecenyl groups, heptadecenyl groups, and octadecenyl groups (these alkenyl groups may be of straight chain or branched form and the position of the double bond is not limited and may be chosen as required).

As said aryl groups, there may be mentioned by way of example aryl groups such as phenyl groups and naphthyl groups.

As said alkylaryl groups, there may be mentioned by way of example alkylaryl groups having a carbon number in the range of from 7 to 18, such as a tolyl group, xylyl group, ethyl phenyl group, propyl phenyl group, butyl phenyl group, pentyl phenyl group, hexyl phenyl group, heptyl phenyl group, octyl phenyl group, nonyl phenyl group, decyl phenyl group, undecyl phenyl group and dodecyl phenyl group (these alkyl groups may be of straight chain or branched form, and the position of substitution into the aryl group is not limited and may be chosen as required).

As said arylalkyl groups, there may be mentioned by way of example arylalkyl groups having a carbon number in the range of from 7 to 12, such as a benzyl group, phenyl ethyl group, phenyl propyl group, phenyl butyl group, phenyl pentyl group and phenyl hexyl group (these alkyl groups may be of straight chain or branched form).

Preferred phosphorus-based compounds include phosphoric acid; phosphorous acid; zinc alkyl dithiophosphates such as zinc dipropyl dithiophosphate, zinc dibutyl dithiophosphate, zinc dipentyl dithiophosphate, zinc dihexyl dithiophosphate, zinc diheptyl dithiophosphate, or zinc dioctyl dithiophosphate (these alkyl groups may be of straight chain form or branched form); monoalkyl esters of phosphoric acid such as monopropyl phosphate, monobutyl phosphate, monopentyl phosphate, monohexyl phosphate, monoheptyl phosphate, or monooctyl phosphate (these alkyl groups may be of straight chain form or branched form); mono(alkyl)aryl esters of phosphoric acid such as monophenyl phosphate and monocresyl phosphate; dialkyl esters of phosphoric acid such as dipropyl phosphate, dibutyl phosphate, dipentyl phosphate, dihexyl phosphate, diheptyl phosphate and dioctyl phosphate (these alkyl groups may be of straight chain form or branched form); di(alkyl)aryl esters of phosphoric acid such as diphenyl phosphate and dicresyl phosphate; trialkyl esters of phosphoric acid such as tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate and trioctyl phosphate (these alkyl groups may be of straight chain form or branched form); tri(alkyl)aryl esters of phosphoric acid such as triphenyl phosphate and tricresyl phosphate; monoalkyl esters of phosphorous acid such as monopropyl phosphite, monobutyl phosphite, monopentyl phosphite, monohexyl phosphite, monoheptyl phosphite and monooctyl phosphite (these alkyl groups may be of straight chain form or branched form); mono(alkyl)aryl esters of phosphorous acid such as monophenyl phosphite and monocresyl phosphite; dialkyl esters of phosphorous acid such as dipropyl phosphite, dibutyl phosphite, dipentyl phosphite, dihexyl phosphite, diheptyl phosphite, and di-octyl phosphite (these alkyl groups may be of straight chain form or branched form); di(alkyl)aryl esters of phosphorous acid such as diphenyl phosphite and dicresyl phosphite; trialkyl esters of phosphorous acid such as tripropyl phosphite, tributyl phosphite, tripentyl phosphite, trihexyl phosphite, triheptyl phosphate and trioctyl phosphite (these alkyl groups may be of straight chain form or branched form); tri(alkyl)aryl esters of phosphorous acid such as triphenyl phosphite, and tricresyl phosphite; and mixtures of these.

Also, as the salts of phosphoric (phosphorous) acid esters, listed above, salts may be conveniently used which are obtained by reacting a nitrogen-containing compound such as ammonia or an amine compound containing in the molecule a hydrocarbon group having a carbon number in the range of from 1 to 8 or a hydroxyl group-containing hydrocarbon group with for example phosphoric acid monoester, phosphoric acid diester, phosphorous acid monoester, or phosphorous acid diester and neutralising part or all of the remaining acidic hydrogen.

Examples of said nitrogen-containing compounds include ammonia; alkylamines such as monomethylamine, monoethylamine, monopropylamine, monobutylamine, monopentylamine, monohexylamine, monoheptylamine, mono-octylamine, dimethylamine, methyl ethylamine, diethylamine, methyl propylamine, ethyl propylamine, dipropylamine, methyl butylamine, ethyl butylamine, propyl butylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine and dioctylamine (these alkyl groups may be of straight chain form or branched form); alkanolamines such as monomethanolamine, monoethanolamine, monopropanolamine, monobutanolamine, monopentanolamine, monohexanolamine, monoheptanolamine, mono-octanolamine, monononanolamine, dimethanolamine, methanol ethanolamine, diethanolamine, methanol propanolamine, ethanol propanolamine, dipropanolamine, methanol butanolamine, ethanol butanolamine, propanol butanolamine, dibutanolamine, dipentanolamine, dihexylanolamine, diheptanolamine and dioctanolamine (these alkanol groups may be of straight chain form or branched form); and mixtures thereof.

Any one or more of the above phosphorus compounds may be blended together in use.

Organic molybdenum-based compounds may be conveniently used as the above anti-wear agent. Typical compounds include molybdenum dithiocarbamates, molybdenum dithiophosphates and amine molybdenates. Molybdenum dithiocarbamates are particularly preferred.

Examples of such molybdenum dithiocarbamates include compounds of general formula (6)

examples of such molybdenum dithiophosphates include compounds of general formula (7)

and examples of such amine molybdenates include compounds of general formula (8)

In the above general formula (6), general formula (7) and general formula (8), R¹² to R²¹ are hydrocarbon groups having a carbon number in the range of from 6 to 18 and may be respectively the same or different. X and Y indicate a sulphur atom or oxygen atom, a≦3, b≦3 and c≦3.

One of said organic molybdenum-based compounds may be employed in the lubricating oil composition of the present invention. Alternatively, two or more of said organic molybdenum-based compounds may be used therein in combination.

The content of said organic molybdenum-based compounds, expressed in terms of the molybdenum content, is preferably at least 200 weight ppm, more preferably in the range of from 400 to 2000 weight ppm, and even more preferably in the range of from 600 to 1000 weight ppm. If the above content of organic molybdenum-based compound is less than 200 weight ppm, then the anti-wear effect may be low; if the content exceeds 2000 weight ppm, the effect of such addition of organic molybdenum-based compounds may become saturated.

As the fatty acid ester compounds and/or aliphatic amine-based compounds of the above anti-wear agent, fatty acid esters, aliphatic amine compounds or any desired mixture of these having straight chain or branched hydrocarbon groups having a carbon number in the range of 6 to 30, preferably having a carbon number in the range of 8 to 24 and even more preferably having a carbon number in the range of 10 to 20 may be employed.

Examples that may be given of such straight chain or branched hydrocarbon groups having a carbon number in the range of 6 to 30 include: alkyl groups such as a hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, eicosyl group, heneicosyl group, docosyl group, tricosyl group, tetracosyl group, pentacosyl group, hexacosyl group, heptacosyl group, octacosyl group, nonacosyl group and triacontyl group, or alkenyl groups such as a hexenyl group, heptenyl group, octenyl group, nonenyl group, decenyl group, undecenyl group, dodecenyl group, tridecenyl group, tetradecenyl group, pentadecenyl group, hexadecenyl group, heptadecenyl group, octadecenyl group, nonadecenyl group, eicosenyl group, heneicosenyl group, docosenyl group, tricosenyl group, tetracosenyl group, pentacosenyl group, hexacosenyl group, heptacosenyl group, octacosenyl group, nonacosenyl group and triacontenyl group. It should be noted that the above alkyl groups and alkenyl groups include all conceivable straight chain constructions and branched chain constructions, and the position of the double bond in the alkenyl groups may be chosen as required.

As the above fatty acid esters, there may be mentioned by way of example esters comprising a fatty acid having a hydrocarbon group as above and an aliphatic monohydric alcohol or an aliphatic polyhydric alcohol. Specific examples of fatty acid esters that may be conveniently used include glycerine mono-oleate, glycerine dioleate, sorbitan mono-oleate and sorbitan dioleate.

Examples of aliphatic amine compounds that may be conveniently used in the lubricating oil composition of the present invention include aliphatic monoamines or their alkylene oxide addition products, aliphatic polyamines or imidazoline compounds, and derivatives thereof. Specific examples of said aliphatic amine compounds include laurylamine, lauryl diethylamine, lauryl diethanolamine, dodecyl dipropanolamine, palmitylamine, stearylamine, stearyl tetramethylene pentamine, oleylamine, oleyl propylene diamine, oleyl diethanolamine, and N-hydroxyethyl oleyl imidazoline, or amine alkylene oxide addition products such as the N, N-dipolyoxyalkylene-N-alkyl (or alkenyl) (having a carbon number in the range of from 6 to 28) addition products of these aliphatic amine compounds, or so-called acid-modified compounds obtained by reacting monocarboxylic acids (fatty acids etc) or oxalic acid, phthalic acid, trimellitic acid, pyromellitic acid or the like polycarboxylic acids having a carbon number in the range of from 2 to 30 with these aliphatic amine compounds and neutralisation or amidation of some or all of the remaining amino groups and/or imino groups. A suitable example is N,N-dipolyoxyethylene-N-oleylamine.

Examples of the aforementioned anti-rust agents include petroleum sulphonates, alkyl benzene sulphonates, dinonyl naphthalene sulphonate, alkenyl succinic acid esters, and polyhydric alcohol esters.

Examples of the aforementioned corrosion inhibitors include benzotriazole-based, tolyl triazole-based, thiadiazole-based and imidazole-based compounds.

The aforementioned oxidation inhibitors include phenyl-based oxidation inhibitors and amine-based oxidation inhibitors.

Preferred examples of phenol-based oxidation inhibitors that may be conveniently used in the lubricating oil composition of the present invention include 4,4′-methylene bis(2,6-di-tert-butyl phenol); 4,4′-bis(2,6-di-tert-butyl phenol), 4,4′-bis(2-methyl-6-tert-butyl phenol); 2,2′-methylene bis(4-ethyl-6-tert-butyl phenol); 2,2′-methylene bis(4-methyl-6-tert-butyl phenol); 4,4′-butylidene bis(3-methyl-6-tert-butyl phenol); 4,4′-isopropylidene bis(2,6-di -tert-butyl phenol); 2,2′-methylene bis(4-methyl-6-nonyl phenol); 2,2′-isobutylidene bis(4,6-dimethyl phenol); 2,2′-methylene bis(4-methyl-6-cyclohexyl phenol); 2,6-di-tert-butyl-4-methyl phenol; 2,6-di-tert-butyl-4-ethyl phenol; 2,4-dimethyl-6-tert-butyl phenol; 2,6-di-tert-a-dimethylamino-p-cresol; 2,6-di-tert-butyl-4(N, N′-dimethylaminomethyl phenol); 4,4′-thiobis(2-methyl-6-tert-butyl phenol); 4,4′-thiobis(3-methyl-6-tert-butyl phenol); 2,2′-thiobis(4-methyl -6-tert-butyl phenol); bis(3-methyl-4-hydroxy-5-tert-butyl benzyl) sulphide; bis(3,5-di-tert-butyl-4-hydroxybenzyl) sulphide; 2,2′-thio-diethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate]; tridecyl-3-(3, 5-di-tert-butyl-4-hydroxyphenyl) propionate; pentaerythrityl-tetrakis [3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate]; octyl-3-(3,5-di -tert-butyl-4-hydroxyphenyl) propionate; octadecyl-3-(3, 5-di-tert-butyl-4-hydroxyphenyl) propionate; or octyl-3-(3-methyl -5-tert-butyl-4-hydroxyphenyl) propionate. One or more of the aforementioned oxidation inhibitors may be used in the lubricating oil composition of the present invention.

Examples of amine-based oxidation inhibitors that may be conveniently used in the lubricating oil composition of the present invention include substituted and non-substituted phenyl-α-naphthylamines, alkyl phenol-α-naphthylamines, and dialkyl diphenylamines. One or more of the aforementioned oxidation inhibitors may be used in the lubricating oil composition of the present invention.

Furthermore, the aforementioned phenol-based oxidation inhibitors and amine-based oxidation inhibitors may be used in combination in the lubricating oil composition of the present invention.

Examples of antifoaming agents that may be conveniently used in the lubricating oil composition of the present invention include a silicone, fluorosilicone, or fluoroalkyl ether.

The present invention further provides the use of the lubricating oil composition of the present invention for lubricating a door closer or a floor hinge. There is also provided a method of lubricating a door closer or a floor hinge comprising using the lubricating oil composition of the present invention to lubricate said door closer or floor hinge.

The lubricating oil composition of the present invention can be conveniently prepared by blending together the base oil having a kinematic viscosity at 40° C. in the range of from 2 to 20 mm²/s and a viscosity index of 50 or more with a polymethacrylate and, optionally, one or more additives as hereinbefore described.

The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the invention in any way.

EXAMPLES Example 1

21.8 parts by weight of mineral oil (B) having a kinematic viscosity of 99.21 mm²/s at 40° C., a kinematic viscosity of 11.14 mm²/s at 100° C., a flash point of 268° C. and a viscosity index of 97 was mixed with 62.2 parts by weight of mineral oil (C) having a kinematic viscosity of 8.74 mm²/s at 40° C., a kinematic viscosity of 2.23 mm²/s at 100° C., a flash point of 160° C. and a viscosity index of 41, to obtain a mixed base oil having a kinematic viscosity of 15.1 mm²/s at 40° C., a kinematic viscosity of 3.22 mm²/s at 100° C. and a viscosity index of 74. This mixed base oil was blended with 16 parts by weight of a polymethacrylate (a) having a weight average molecular weight of 270,000.

The resulting lubricating oil composition had a kinematic viscosity 68.8 mm²/s at 40° C., a kinetic viscosity of 17.92 mm²/s at 100° C., a viscosity index of 281, a pour point of less than −50° C., a CCS viscosity at −20° C. of 1120 mPas, and a flash point of 156° C.

This lubricating oil composition had fully satisfactory properties for use as a hydraulic oil composition for a door closer from the low temperature region to the high temperature region.

As an oil seal compatibility test, an immersion test of 1000 hours at oil temperature of 100° C. was conducted on said lubricating oil composition in accordance with the procedure of JIS K 6258 “Method of immersion testing of vulcanised rubber”, and the external appearance and physical properties of the oil seal determined after conducting the test, in order to evaluate compatibility. Excellent results were obtained with said lubricating oil composition and compatibility with the oil seal was confirmed.

Example 2

20 parts by weight of a mineral oil (A) having a kinematic viscosity of 24.98 mm²/s at 40° C., a kinematic viscosity of 4.64 mm²/s at 100° C., a flash point of 222° C. and a viscosity index of 101 was mixed with 63.7 parts by weight of a mineral oil (E) having a kinematic viscosity of 4.22 mm²/s at 40° C., a kinematic viscosity of 1.51 mm/s at 100° C., a flash point of 142° C., to obtain a mixed base oil having a kinematic viscosity of 5.93 mm²/s at 40° C., a kinematic viscosity of 1.89 mm²/s at 100° C. and a viscosity index of 108. This mixed base oil was blended with 16.3 parts by weight of a polymethacrylate (b) having a weight average molecular weight of 400,000.

The resulting lubricating oil composition had a kinematic viscosity of 29.86 mm²/s at 40° C., a kinematic viscosity of 10.49 mm²/s at 100° C., a viscosity index of 367, a pour point of less than −50° C., a CCS viscosity at −20° C. of 1900 mPas, and a flash point of 146° C.

This lubricating oil composition had fully satisfactory properties for use as a hydraulic oil composition for a door closer from the low temperature region to the high temperature region and also showed excellent results in the above oil seal compatibility test.

Example 3

21.3 parts by weight of a mineral oil (B) having a kinematic viscosity of 99.21 mm²/s at 40° C., a kinematic viscosity of 11.14 mm²/s at 100° C. and a flash point of 268° C. was mixed with 62.2 parts by weight of a mineral oil (C) of kinematic viscosity of 8.74 mm2/s at 40° C., kinematic viscosity of 2.23 mm²/s at 100° C., a flash point 160° C. and a viscosity index of 41, to obtain a mixed base oil having a kinematic viscosity of 15.1 mm²/s at 40° C., a kinematic viscosity of 3.22 mm²/s at 100° C. and a viscosity index of 74.

This mixed base oil was blended with 16 parts by weight of a polymethacrylate (a) of weight average molecular weight 270,000, 0.2 parts by weight of the phosphorus compound TCP (tricresyl phosphate) as anti-wear agent, 0.3 parts by weight of hindered phenol based oxidation inhibitor, 0.05 parts by weight of a oxyalkyl carboxylic acid ester (content 70%) and 0.001 parts by weight of antifoaming agent dimethyl siloxane.

The resulting lubricating oil composition had a kinematic viscosity of 67.4 mm²/s at 40° C., a kinematic viscosity of 18.0 mm²/s at 100° C., a viscosity index of 288, a pour point of less than −50° C., a CCS viscosity at −20° C. of 1080 mPas, and a flash point of 156° C.

This lubricating oil composition had fully satisfactory properties for use as a hydraulic oil composition for a door closer from the low temperature region to the high temperature region and also showed excellent results in the above oil seal compatibility test.

Example 4

20 parts by weight of a mineral oil (A) having a kinematic viscosity of 24.98 mm²/s at 40° C., a kinematic viscosity of 4.64 mm²/s at 100° C. and a flash point of 222° C. were mixed with 63 parts by weight of a mineral oil (E) of kinematic viscosity of 4.22 mm²/s at 40° C., a kinematic viscosity of 1.51 mm²/s at 100° C., and a flash point of 142° C., to obtain a mixed base oil having a kinematic viscosity of 5.93 mm²/s at 40° C., a kinematic viscosity of 1.89 mm²/s at 100° C. and a viscosity index of 108. This mixed base oil was blended with 16.3 parts by weight of polymethacrylate (b) having a weight average molecular weight of 400,000, 0.5 parts by weight of the phosphorus compound TCP (tricresyl phosphate) as anti-wear agent, 0.2 parts by weight of the organic molybdenum compound molybdenum dialkyl thiophosphate and 0.001 parts by weight of antifoaming agent dimethyl siloxane.

The resulting lubricating oil composition had a kinematic viscosity of 29.39 mm²/s at 40° C., a kinematic viscosity of 10.53 mm²/s at 100° C., a viscosity index of 375, a pour point less than −50° C., a CCS viscosity at −20° C. of 1890 mPas, and a flash point of 146° C.

This lubricating oil composition had fully satisfactory properties for use as a hydraulic oil composition for a door closer from the low temperature region to the high temperature region and also showed excellent results in the above oil seal compatibility test.

Example 5

6.5 parts by weight of a mineral oil (B) having a kinematic viscosity of 99.21 mm²/s at 40° C., a kinematic viscosity of 11.14 mm²/s at 100° C., a flash point of 268° C. and a viscosity index of 97 was mixed with 24.4 parts by weight of a mineral oil (C) having a kinematic viscosity of 8.74 mm²/s at 40° C., a kinematic viscosity of 2.23 mm²/s at 100° C., a flash point of 160° C. and a viscosity index of 41, 36.7 parts by weight of “XHVI” oil (“XHVI” is a trade mark for synthetic hydrocarbon base oils sold by the Shell Group) having a kinematic viscosity of 23.6 mm²/s at 40° C., a kinematic viscosity of 5.51 mm²/s at 100° C., a flash point of 244° C. and a viscosity index 148, and 7.35 parts by weight of DOA (dioctyl adipate) to obtain a mixed base oil having a kinematic viscosity of 15.03 mm²/s at 40° C., a kinematic viscosity of 3.49 mm²/s at 100° C. and a viscosity index of 109.

This mixed base oil was blended with 24.5 parts by weight of a polymethacrylate (a) having a weight average molecular weight of 270,000, 0.2 parts by weight of the phosphorus compound TCP (tricresyl phosphate) as anti-wear agent, 0.3 parts by weight of a hindered phenol based oxidation inhibitor, 0.05 parts by weight of an oxyalkyl carboxylic acid ester (content 70%) and 0.001 parts by weight of antifoaming agent dimethyl siloxane.

The resulting lubricating oil composition had a kinematic viscosity of 28.6 mm²/s at 40° C., a kinematic viscosity of 10.15 mm²/s at 100° C., a viscosity index of 314, a pour point −45° C., a CCS viscosity at −20° C. of 1450 mPas, and a flash point of 182° C.

This lubricating oil composition had fully satisfactory properties for use as a hydraulic oil composition for a door closer from the low temperature region to the high temperature region and also showed excellent results in the above oil seal compatibility test.

Example 6

48.73 parts by weight of mineral oil (C) having a kinematic viscosity of 8.74 mm²/s at 40° C., a kinematic viscosity of 2.23 mm²/s at 100° C., a flash point of 160° C. and a viscosity index of 41 was mixed with 29.74 parts by weight of a mineral oil (D) having a kinematic viscosity of 19.24 mm²/s at 40° C., a kinematic viscosity of 4.19 mm/s at 100° C., a flash point of 234° C. and a viscosity index of 123, to obtain a mixed base oil having a kinematic viscosity of 11.93 mm²/s at 40° C., a kinematic viscosity of 2.85 mm²/s at 100° C. and a viscosity index of 81. To this mixed base oil were added 20.98 parts by weight of a polymethacrylate (a) having a weight average molecular weight of 270,000, 0.2 parts by weight of phosphorus compound TCP (tricresyl phosphate) as anti-wear agent, 0.3 parts by weight of a hindered phenol based oxidation inhibitor, 0.05 parts by weight of an oxyalkyl carboxylic acid ester (content 70%) and 0.001 parts by weight of antifoaming agent dimethyl siloxane.

The resulting lubricating oil composition had a kinematic viscosity of 71.76 mm²/s at 40° C., a kinematic viscosity of 21.48 mm²/s at 100° C., a viscosity index of 323, a pour point of less than −50° C., a CCS viscosity at −20° C. of 660 mPas, and flash point of 160° C.

This lubricating oil composition had fully satisfactory properties for use as a hydraulic oil composition for a door closer from the low temperature region to the high temperature region and also showed excellent results in the above oil seal compatibility test.

Example 7

56.89 parts by weight of a mineral oil (C) having a kinematic viscosity of 8.74 mm²/s at 40° C., a kinematic viscosity of 2.23 mm²/s at 100° C., a flash point of 160° C. and a viscosity index of 41, 7.86 parts by weight of a mineral oil (E) of kinematic viscosity of 4.22 mm²/s at 40° C., a kinematic viscosity of 1.51 mm²/s at 100° C., a flash point of 142° C., and 10 parts by weight of poly-α-olefin (PAO) of kinematic viscosity of 34.87 mm2/s at 40° C., a kinematic viscosity of 6.38 mm²/s at 100° C. and a viscosity index of 136 were mixed to obtain a mixed base oil of a kinematic viscosity of 9.56 mm²/s at 40° C., a kinematic viscosity 2.44 mm²/s at 100° C. and a viscosity index 71.

This mixed base oil was blended with 24.66 parts by weight of a polymethacrylate (a) having a weight average molecular weight of 270,000, 0.2 parts by weight of the phosphorus compound TCP (tricresyl phosphate) as anti-wear agent, 0.3 parts by weight of a hindered phenol based oxidation inhibitor, 0.05 parts by weight of a oxyalkyl carboxylic acid ester (content 70%) and 0.001 parts by weight of antifoaming agent dimethyl siloxane.

The resulting lubricating oil composition had a kinematic viscosity of 80.38 mm²/s at 40° C., a kinematic viscosity of 24.88 mm²/s at 100° C., a viscosity index of 335, pour point of less than −50° C., a CCS viscosity at −20° C. of 730 mPas, and a flash point of 150° C.

This lubricating oil composition had fully satisfactory properties for use as a hydraulic oil composition for a door closer from the low temperature region to the high temperature region and also showed excellent results in the above oil seal compatibility test.

Example 8

44.26 parts by weight of mineral oil (E) having a kinematic viscosity of 4.22 mm²/s at 40° C., a kinematic viscosity of 1.51 mm²/s at 100° C., a flash point of 142° C., and 25.36 parts by weight of a poly-α-olefin (PAO) having a kinematic viscosity of 34.87 mm²/s at 40° C., a kinematic viscosity of 6.38 mm²/s at 100 degrees, a flash point of 258° C. and a viscosity index of 136 were mixed to obtain a mixed base oil having a kinematic viscosity of 8.31 mm²/s at 40° C., a kinematic viscosity of 2.42 mm²/s at 100° C. and a viscosity index of 118.

This mixed base oil was blended with 29.83 parts by weight of a polymethacrylate (a) having a weight average molecular weight of 270,000, 0.2 parts by weight of the phosphorus compound TCP (tricresyl phosphate) as anti-wear agent, 0.3 parts by weight of a hindered phenol based oxidation inhibitor, 0.05 parts by weight of oxyalkyl carboxylic acid ester (content 70%) and 0.001 parts by weight of antifoaming agent dimethyl siloxane.

The resulting lubricating oil composition had a kinematic viscosity of 88.97 mm²/s at 40° C., a kinematic viscosity of 8.49 mm²/s at 100° C., a viscosity index of 347, a pour point of less than −50° C., a CCS viscosity at −20° C. of 730 mPas, and a flash point of 150° C.

This lubricating oil composition had fully satisfactory properties for use as a hydraulic oil composition for a door closer from the low temperature region to the high temperature region and also showed excellent results in the above oil seal compatibility test.

Example 9

10.2 parts by weight of a mineral oil (A) having a kinematic viscosity of 24.98 mm²/s at 40° C., a kinematic viscosity of 4.64 mm²/s at 100° C., a flash point of 222° C. and a viscosity index of 101 was mixed with 50.75 parts by weight of a mineral oil (C) having a kinematic viscosity of 8.74 mm²/s at 40° C., a kinematic viscosity of 2.23 mm²/s at 100° C., a flash point of 160° C. and a viscosity index 41, and with 20.3 parts by weight of a mineral oil (D) having a kinematic viscosity of 19.24 mm²/s at 40° C., a kinematic viscosity of 4.19 mm²/s at 100° C., a flash point of 234° C. and a viscosity index of 123, to obtain a mixed base oil having a kinematic viscosity of 12.16 mm²/s at 40° C., a kinematic viscosity of 2.87 mm²/s at 100° C. and a viscosity index 78.

This mixed base oil was blended with 18.2 parts by weight of a polymethacrylate (a) having a weight average molecular weight of 270,000, 0.2 parts by weight of the phosphorus compound TCP (tricresyl phosphate) as anti-wear agent, 0.3 parts by weight of a hindered phenol based oxidation inhibitor, 0.05 parts by weight of an oxyalkyl carboxylic acid ester (content 70%) and 0.001 parts by weight of antifoaming agent dimethyl siloxane.

The resulting lubricating oil composition had a kinematic viscosity of 61.59 mm²/s at 40° C., a kinematic viscosity of 18.22 mm²/s at 100° C., a viscosity index of 315, a pour point of less than −50° C., a CCS viscosity at −20° C. of 660 mPas, and a flash point of 160° C.

This lubricating oil composition had fully satisfactory properties for use as a hydraulic oil composition for a door closer from the low temperature region to the high temperature region and also showed excellent results in the above oil seal compatibility test.

Example 10

9.8 parts by weight of a mineral oil (A) having a kinematic viscosity of 24.98 mm²/s at 40° C., a kinematic viscosity of 4.64 mm²/s at 100° C., a flash point of 222° C. and a viscosity index of 101 was mixed with 63.9 parts by weight of a mineral oil (E) having a kinematic viscosity of 4.22 mm²/s at 40° C., a kinematic viscosity of 1.51 mm²/s at 100° C., and a flash point of 142° C., to obtain a mixed base oil having a kinematic viscosity of 5.11 mm²/s at 40° C., a kinematic viscosity of 1.71 mm²/s at 100° C. and a viscosity index of 109.

This mixed base oil was blended with 24.6 parts by weight of a polymethacrylate (a) having a weight average molecular weight of 270,000, 0.5 parts by weight of the phosphorus compound TCP (tricresyl phosphate) as anti-wear agent, 1.0 parts by weight of hindered phenol based oxidation inhibitor, 0.2 parts by weight of the organic molybdenum compound molybdenum dialkyl thiophosphate and 0.001 parts by weight of antifoaming agent dimethyl siloxane.

The resulting lubricating oil composition had a kinematic viscosity of 52.16 mm²/s at 40° C., a kinematic viscosity of 19.58 mm²/s at 100° C., a viscosity index of 390, a pour point of less than −50° C., a CCS viscosity at −20° C. of 2350 mPas, and a flash point of 142° C.

This lubricating oil composition had fully satisfactory properties for use as a hydraulic oil composition for a door closer from the low temperature region to the high temperature region and also showed excellent results in the above oil seal compatibility test.

Comparative Example 1

79.45 parts by weight of a mineral oil (F) having a kinematic viscosity of 8.66 mm²/s at 40° C., a kinematic viscosity of 2.19 mm²/s at 100° C., a flash point of 136° C. and a viscosity index of 30 was mixed with 20 parts by weight of a polymethacrylate (a) having a weight average molecular weight of 270,000, 0.2 parts by weight of the phosphorus compound TCP (tricresyl phosphate) as anti-wear agent, 0.3 parts by weight of a hindered phenol based oxidation inhibitor, 0.05 parts by weight of an oxyalkyl carboxylic acid ester (content 70%) and 0.001 parts by weight of antifoaming agent dimethyl siloxane.

The resulting lubricating oil composition had a kinematic viscosity of 53.49 mm²/s at 40° C., a kinematic viscosity of 7.19 mm²/s at 100° C., a viscosity index of 339, a pour point of less than −50° C., CCS viscosity at −20° C. of 925 mPas, and a flash point of 128° C.

This lubricating oil composition was found to be lacking in compatibility in the above oil seal compatibility test and was of low flashpoint and was consequently unsuitable for use as a hydraulic oil composition for a door closer.

Comparative Example 2

79.45 parts by weight of a mineral oil (F) having a kinematic viscosity of 8.66 mm²/s at 40° C., a kinematic viscosity of 2.19 mm²/s at 100° C., a flash point of 136° C. and a viscosity index of 30 was mixed with 20 parts by weight of a polymethacrylate (a) having a weight average molecular weight of 400,000, 0.2 parts by weight of the phosphorus compound TCP (tricresyl phosphate) as anti-wear agent, 0.3 parts by weight of a hindered phenol based oxidation inhibitor, 0.05 parts by weight of an oxyalkyl carboxylic acid ester (content 70%) and 0.001 parts by weight of antifoaming agent dimethyl siloxane.

The resulting lubricating oil composition had a kinematic viscosity of 55.32 mm²/s at 40° C., a kinematic viscosity of 15.9 mm²/s at 100° C., a viscosity index of 304, a pour point less than −50° C., a CCS viscosity at −20° C. of 810 mpas, and a flash point of 128° C.

This lubricating oil composition was found to be lacking in compatibility in the above oil seal compatibility test and was of low flashpoint and was consequently unsuitable for use as a hydraulic oil composition for a door closer.

Comparative Example 3

89.45 parts by weight of mineral oil (A) having a kinematic viscosity of 24.98 mm²/s at 40° C., a kinematic viscosity of 4.64 mm²/s at 100° C., a flash point of 222° C. and a viscosity index of 101 was mixed with 10 parts by weight of a polymethacrylate (a) having a weight average molecular weight of 270,000, 0.2 parts by weight of the phosphorus compound TCP (tricresyl phosphate) as anti-wear agent, 0.3 parts by weight of a hindered phenol based oxidation inhibitor, 0.05 parts by weight of an oxyalkyl carboxylic acid ester (content 70%) and 0.001 parts by weight of antifoaming agent dimethyl siloxane.

The resulting lubricating oil composition had a kinematic viscosity of 58 mm²/s at 40° C., a kinematic viscosity of 13.81 mm²/s at 100° C., a viscosity index of 249, a pour point of −45° C., a CCS viscosity at −20° C. of 3050 mpas, and a flash point 128° C.

Whilst this lubricating oil composition was found to be compatible in the above oil seal compatibility test, it had a high CCS viscosity at −20° C. and was consequently unsuitable for use as a hydraulic oil composition for a door closer.

Comparative Example 4

79.45 parts by weight of a poly-α-olefin (PAO) having a kinematic viscosity of 34.87 mm²/s at 40° C., a kinematic viscosity of 6.38 mm²/s at 100 degrees, a flash point of 258° C. and a viscosity index of 136 was mixed with 20 parts by weight of a polymethacrylate (a) having a weight average molecular weight of 270,000, 0.2 parts by weight of the phosphorus compound TCP (tricresyl phosphate) as anti-wear agent, 0.3 parts by weight of a hindered phenol based oxidation inhibitor, 0.05 parts by weight of an oxyalkyl carboxylic acid ester (content 70%) and 0.001 parts by weight of antifoaming agent dimethyl siloxane.

The resulting lubricating oil composition kinematic viscosity of 93.31 mm²/s at 40° C., a kinematic viscosity of 22.48 mm²/s at 100° C., a viscosity index of 270, a pour point of less than −50° C., a CCS viscosity at −20° C. of 3450 mPas, and a flash point of 250° C.

This lubricating oil composition had a high CCS viscosity at −20° C., and produced shrinkage of the oil seal, and was therefore unsuitable for use as hydraulic oil composition for a door closer. 

1. A lubricating oil composition comprising a base oil having a kinematic viscosity at 40° C. in the range of from 2 to 20 mm²/s and a viscosity index of 50 or more and a polymethacrylate, wherein the lubricating oil composition has a kinematic viscosity at 40° C. in the range of from 22 to 95 mm²/s; a kinematic viscosity at 100° C. in the range of from 10 to 30 mm²/s; a pour point of −10° C. or less; a CCS viscosity at −20° C. of 2500 mPas or less; and a flash point of 140° C. or more.
 2. The lubricating oil composition of claim 1 wherein the weight average molecular weight of the polymethacrylate is in the range of from 150,000 to 700,000.
 3. The lubricating oil composition of claim 2 wherein the weight average molecular weight of the polymethacrylate is in the range of from 200,000 to 500,000.
 4. The lubricating oil composition of claim 1 wherein the viscosity index of the base oil is 70 or more.
 5. The lubricating oil composition of claim 1 wherein the lubricating oil composition further comprises at least one type of additive selected from an anti-wear agent, an antioxidant, an anti-rust agent, a corrosion inhibitor and an antifoaming agent.
 6. The lubricating oil composition of claim 1 wherein said lubricating oil composition is a hydraulic oil composition for a door closer or a hydraulic oil composition for a floor hinge or both.
 7. The lubricating oil composition of claim 2 wherein the viscosity index of the base oil is 70 or more.
 8. The lubricating oil composition of claim 7 wherein the lubricating oil composition further comprises at least one type of additive selected from an anti-wear agent, an antioxidant, an anti-rust agent, a corrosion inhibitor and an antifoaming agent.
 9. The lubricating oil composition of claim 5 wherein said lubricating oil composition is a hydraulic oil composition for a door closer or a hydraulic oil composition for a floor hinge or both.
 10. A method of lubricating a door closer or a floor hinge comprising using a lubricating oil composition of claim 1 to lubricate said door closer or floor hinge.
 11. A method of lubricating a door closer or a floor hinge comprising using a lubricating oil composition of claim 2 to lubricate said door closer or floor hinge.
 12. A method of lubricating a door closer or a floor hinge comprising using a lubricating oil composition of claim 4 to lubricate said door closer or floor hinge.
 13. A method of lubricating a door closer or a floor hinge comprising using a lubricating oil composition of claim 7 to lubricate said door closer or floor hinge.
 14. A method of lubricating a door closer or a floor hinge comprising using a lubricating oil composition of claim 8 to lubricate said door closer or floor hinge. 